Remove old default search preferences.

components/search_engines/default_search_pref_migration.h

Index: components/search_engines/default_search_pref_migration.h
diff --git a/components/search_engines/default_search_pref_migration.h b/components/search_engines/default_search_pref_migration.h
deleted file mode 100644
index b2fd0c443fc18d740f4a7379319db155d078dda1..0000000000000000000000000000000000000000
--- a/components/search_engines/default_search_pref_migration.h
+++ /dev/null
@@ -1,17 +0,0 @@
-// Copyright 2014 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef COMPONENTS_SEARCH_ENGINES_DEFAULT_SEARCH_PREF_MIGRATION_H_
-#define COMPONENTS_SEARCH_ENGINES_DEFAULT_SEARCH_PREF_MIGRATION_H_
-
-class PrefService;
-
-// Migrates a DSE value stored in separate String/List/..Value preferences by
-// M35 or earlier to the new single DictionaryValue used in M36.
-// Operates immediately if |pref_service| is fully initialized. Otherwise, waits
-// for the PrefService to load using an observer.
-void ConfigureDefaultSearchPrefMigrationToDictionaryValue(
-    PrefService* pref_service);
-
-#endif  // COMPONENTS_SEARCH_ENGINES_DEFAULT_SEARCH_PREF_MIGRATION_H_